Swimmers, especially female swimmers, face an energy balance
conundrum. Elite swimmers typically undertake 4000-20,000 m per day in
training, burning thousands of calories. However, the typical body fat
levels of these athletes are significantly higher than runners or cyclists
who expend similar or even smaller amounts of energy in their training.
Many female swimmers have fought well-publicized battles with their body
fat levels and with their coaches! They are generally prescribed "land
training" (running or cycling) in addition to their many laps of the
pool in the belief that it is a necessary treatment to produce lower skinfold
levels.

Do energy discrepancies really exist in swimming? Why do swimmers seem
to have drawn the short straw of body fat management? The following theories
have been suggested:

Swimmers have higher energy intakes than other athletes and eat
more energy than they expend. It has been suggested that swimming doesn't
cause the appetite drop that accompanies heavy running and cycling training.
Many people observe that they feel like "eating a horse" after
they have finished a swim training session, and may overcompensate for
the energy they have just burned. Some research suggests that this is due
to the cool temperatures in which swimmers train. By contrast, runners
and cyclists usually experience an increase in body temperature during
training, which may serve to suppress appetite - at least in the short
term.

Swimmers are less active outside their training sessions. They are
so tired from the hours spent training that they sleep, sit or otherwise
avoid any real energy expenditure outside their sessions.

Two studies from Costill's Human Performance Laboratory at Ball State
University have tried to address the energy balance oddity of swimmers.
Jang et al.(1987) attempted to gain a crude measure
of daily energy balance by comparing collegiate swimmers and collegiate
distance runners. Ten athletes of each sex from each sport participated
in the study. The findings: runners had lower body fat levels than swimmers
(7% v 12% for male runners v swimmers, and 15% v 20% for females). All
subjects kept detailed 3-day food records, and 1-day activity records were
kept by half the subjects in each group. These records noted the amount
of time each individual spent sleeping, sitting, walking, standing or training.
The energy cost of these activities was estimated individually for each
athlete by duplicating the activity in the laboratory and collecting oxygen
consumption data. This factor multiplied by the time spent in each activity
produced an estimate of total daily energy expenditure.

Results showed that both groups reported similar daily energy intakes:
3380 kcal and 3460 kcal for male swimmers and runners; 2490 kcal and 2040
kcal for female swimmers and runners, respectively. Estimated energy output
was in agreement for each group, with the values for the groups of male
athletes being roughly equal and similar to their reported intake. The
female swimmers had a higher energy expenditure than female runners, and
in fact were in slight negative energy balance. These results were not
helpful in finding or explaining an energy dilemma, or major differences
between types of athletes. The theories above might explain the problems
experienced by some individual swimmers, but the theories were not supported
by evidence from the study.

One of the limitations of this study is that each method of measuring
energy balance is subject to considerable flaws. It is almost impossible
to measure usual energy intake from diaries. Apart from the errors in translating
descriptions of food into calorie counts, it is unlikely that people eat
"normally" while they are recording. It is well-known that those
who are conscious of their body fat underreport their food intake. It is
also hard to complete and describe "normal" by record. In reporting,
athletes try to appear as "good" as possible and thereby cover-up
the clues to any energy balance problems. The behavior of individuals may
also be masked by the "averaging" of results.

The other study by Flynn et al.(1990) examined
energy and fuel usage during training sessions and recovery in swimming
and running. It theorized that differences in hormonal patterns and the
oxidation of fat might explain differences in body fat levels. Swimmers
and runners trained for 45 minutes at 75-80% V02max then recovered for
2 hours. Triathletes did one session of each so that results could be compared
for the same individual. During these periods, blood hormone levels, glucose
and fatty acid levels, and gas exchange were measured and oxidation of
various body fuels monitored.

The results showed no differences in total energy expenditure during
training or recovery between groups. There were some differences in substrate
utilization and hormone levels. For example, swimming resulted in lower
blood glucose levels than running, with some evidence of a greater reliance
on carbohydrate as a fuel during swimming. This is likely to be further
accentuated in the real life training of swimmers who undertake a high
proportion of high-intensity interval work. During recovery, fat oxidation
tended to be greater after swimming than running. Overall, these differences
were small and could not explain why swimmers have higher body fat levels.

While theories abound, no studies can verify or explain a real difference.
These studies clearly leave the way open for further research. Techniques
such as the double-labelled water method of energy expenditure estimation
might provide a new way to measure energy balance issues. A final idea
that needs to be explored is whether a selection process is at hand. Elite
swimmers may be predisposed to have higher body fat levels because it is
a help, or at least less of a disadvantage, to their swimming. Rounded
shoulders and smooth curves may be more biomechanically sound than bony
angles. Higher body fat levels are a greater disadvantage to weight-bearing
sports like running. So perhaps those who aren't genetically inclined to
very low body fat levels, but are otherwise possessive of high-level endurance
qualities, should head for the water at an early age!